Reservoir models, which may be used to predict fluid flow as well as hydrocarbon in place, can be built at a variety of scales, or cell sizes. Typically, a relatively “fine scale” model may be built in a geological modeling package, and may consist of many millions of cells. This model may then be “upscaled” to a relatively “coarse scale” model for use in, for example, dynamic reservoir simulation packages.
Using conventional techniques, however, there is a possibility that some of the coarsened grid cells may initially be defined by one or more complex quadrilaterals, causing so-called “self-intersecting” or “inside-out” cells. Such self-intersecting (or inside-out) cells make no sense to reservoir simulation models and typically cause simulation errors or failures. Identification and removal of inside-out cells typically requires time-consuming and expensive manual activities. In addition, using conventional techniques, the resulting coarsened grid may not be comparable to the underlying fine grid on a node-by-node basis, such that a comparison of simulation results on a coarse grid versus on the underlying fine grid is only at best approximate. Therefore, although desirable results have been achieved using such conventional techniques, there is room for improvement.